As judged by guanine nucleotide exchange, the multi-receptor (R) system in the turkey erythrocyte (TE) plasma membrane shows that adenosine has access to fewer regulatory components (N), at a slower rate than does isoproterenol. Adenosine inhibition is mediated through the P site by a process not involving nucleotide exchange. By the use of a complementation assay it was shown that the TE system can function adequately as an acceptor for N. Irradiation analysis of the TE system shows that it consists of a multi-subunit form of R and a multi-subunit form of N, linked to the catalytic unit in a precoupled complex in the plasma membrane.